Spring carrier with adustable spring collar

ABSTRACT

A spring carrier for mounting a spring strut to a vehicle body includes a vibration damper having a cylinder and a piston rod which is axially guided in the cylinder, first and second spring collars, and a spring located between the spring collars. An actuator includes a nut and a threaded spindle surrounding the piston rod, the actuator being driven to change the relative axial position of the spring collars. A guide tube extends coaxially between the piston rod and the threaded spindle, the guide tube being fixed to the vehicle body by a first resilient mount, the piston rod being fixed to the guide tube by a second resilient mount, whereby the piston rod can move relative to the first resilient mount.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to spring carrier for mounting a spring strut to avehicle, including a vibration damper including a cylinder and a pistonrod which is axially guided in the cylinder, first and second springcollars with a spring therebetween, and an actuator which is driven tochange the relative axial position of the spring collars.

2. Description of the Related Art

A vehicle chassis which comprises a spring carrier with an adjustablespring collar for a suspension spring is known from DE 102 55 764 B3,which represents the underlying state of the art. To actuate the springcollar, an actuator designed as an electric motor is used, which drivesa hollow threaded spindle. A threaded nut is mounted on the actuatingthread of the threaded spindle, and this nut is connected in turn to anadjustable spring collar. The rotary motion of the rotor is converted bythe combination of the spindle and the threaded nut into an axial motionof the spring collar. In the case of a passenger vehicle, for example, asuspension spring must support one-quarter of the entire load of thevehicle. The spring force is transmitted via the threaded nut/threadedspindle combination to the rotor and from there to the housing of theelectric motor, which is connected by a resilient mount with bothangular and impact resilience to a vehicle body.

A piston rod of a conventional vibration damper extends through thehollow threaded spindle. An axial bearing, which allows the piston rod acertain freedom of movement with respect to the vehicle body, is mountedon the outer end of the piston rod. The piston rod is attached to themount by way of a cup-shaped component, against which the housing of theactuator is also supported. It follows from this that no relativemovement can occur between the piston rod and the actuator.

The high-frequency damping forces which occur in the vibration damperare transmitted via the resilient mount to the vehicle body. Because ofthe spring forces which are present, the resilient mount is designed tobe so stiff that the damping forces are transmitted almost unsprung tothe vehicle body, where clearly audible noises occur.

Any transverse forces which the suspension spring may transmit to thethreaded spindle are absorbed by the piston rod of the vibration damper,acting via a needle bearing. As a result, however, a transverse force isgenerated inside the vibration damper, which leads to an increase in thefriction between the piston rod and the piston rod guide (not shown). Asa result, the increase in static friction in the vibration damper leadsto a loss of driving comfort.

Another disadvantage of this spring carrier is that it is very difficultto remove the vibration damper when it needs to be repaired. For thispurpose, the entire spring carrier must be removed from the vehiclefirst. Then the housing with the stator and a retaining ring can beremoved so that then the piston rod can be pulled from the threadedspindle. On closer consideration, it is obvious that the installation ofthe vibration damper must also be rather complicated, because the thruststop is peened onto the piston rod, and the threaded spindle has a muchsmaller inside diameter than the outside diameter of the thrust stop.

SUMMARY OF THE INVENTION

The task of the present invention is to realize a spring carrier whichcan be assembled easily with a vibration damper and to ensure that thevibration damper is supported with the greatest possible elasticity.

According to the invention, a guide tube proceeds from the firstresilient mount and extends between the piston rod and the threadedspindle, and a second resilient mount having both angular and impactresistance is installed between the piston rod and the guide tube sothat the piston rod can move relative to the first resilient mount. Thesecond mount consists essentially of an elastomeric material, but mayalso be an axially movable ball bearing in combination with a spring,for example a Belleville spring.

The second resilient mount can absorb the high-frequency excitations ofthe piston rod caused by the damping forces, so that no bothersomenoises are transmitted to the body of the vehicle.

The damping forces are usually much weaker than the supporting forces ofthe suspension spring of the spring strut unit. For this reason, thespring rate of the resilient mount of the piston rod can be lower thanthat of the resilient mount of the guide tube.

The guide tube has a cup-shaped expansion to hold the mount for thepiston rod. The guide tube also has a mounting surface for the firstresilient mount. The first and second resilient mounts are arrangedfunctionally in series, but as a result of the difference between theirspring rates, there is a clear-cut functional separation between them.At the same time, the guide tube creates an interconnected structuralunit containing both mounts.

The mounting surface for the first resilient mount is provided on amounting flange of the guide tube. This surface extends both axially andradially, and is preferably conical. The mounting flange can be used asa central fastening element inside the spring strut.

According to an advantageous embodiment, the actuator is designed as arotary drive, and the threaded spindle is supported radially against theguide tube. The guide tube prevents the threaded spindle from beingdeformed by the force of the springs and thus from generating clampingforces together with the threaded nut. The great advantage is alsooffered that the vibration damper can be installed and removed withoutthe need for any work on the actuator, for example.

A bearing for the rotor of the rotary drive can also be supportedagainst the mounting flange. This variant guarantees that the threadedspindle will run with precise concentricity, because the threadedspindle and the rotor are both centered by the same component.

The guide tube can be divided at a certain point along its length. Bymeans of this measure, it is easier to gain access to the bearingslocated between the threaded spindle and the guide tube.

It is also possible to connect the guide tube to the housing of theactuator. This provides the guide tube with a very strong mounting.

With respect to the assembly of the vibration damper, it is especiallyadvantageous for a thrust stop to be attached to the guide tube, thisstop going into effect when the piston rod reaches a certain point alongthe course of its inward travel. A thrust stop is often attached to thepiston rod outside the cylinder. The thrust stop could thus interferewith the course of the assembly work, especially when the piston rod ispushed into the guide tube. This problem does not occur with the newsolution.

Other objects and features of the present invention will become apparentfrom the following detailed description considered in conjunction withthe accompanying drawings. It is to be understood, however, that thedrawings are designed solely for purposes of illustration and not as adefinition of the limits of the invention, for which reference should bemade to the appended claims. It should be further understood that thedrawings are not necessarily drawn to scale and that, unless otherwiseindicated, they are merely intended to conceptually illustrate thestructures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross section of a spring strut according to theinvention;

FIG. 2A shows a half cross sectional of the spring strut of FIG. 1 witha thrust stop; and

FIG. 2B shows a half cross section of the spring strut of FIG. 1 with adivided guide tube.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1 shows the upper part of a spring strut 1, which is installed, forexample, between a vehicle axle (not shown) and a vehicle body. Avibration damper 3, known in and of itself, includes an axially movablepiston rod 5 in a cylinder 7, and is surrounded by a first spring 9 anda second spring 11. The first spring 9 is clamped between a first springcollar 13 and a second spring collar 15. The second spring 11 is locatedbetween the bottom side of the second spring collar 15 and a thirdspring collar (not shown), which is attached optionally either to thecylinder 7 or to a part of the vehicle axle. The upper spring collar 13is connected by a universally resilient mount 17 to the vehicle body. Arotary drive 19 in the form of an electric motor is also attached tothis head bearing. The rotary drive comprises a housing 21 with an endpart 23, which forms a one-piece unit with the upper spring collar 13.

In the housing 21, a ring-shaped stator 25 is installed, which drives arotor 27 with a U-shaped cross section. A threaded spindle 31 isattached to an axial sidepiece 29 of the rotor 27; the outer lateralsurface of this spindle has an actuating thread 33. A threaded nut 35engages in the actuating thread 33, this nut being in working connectionwith the second spring collar 15 by way of an intermediate sleeve 37. Asa function of the rotational movement of the rotor 27 and thus of thethreaded spindle 31, the threaded nut 35 executes translational axialmovement, which is accompanied by the synchronous movement of the secondspring collar 15, as a result of which the overall spring force of thetwo springs 9, 11 can be adjusted to compensate, for example, for arolling motion of the vehicle body.

Starting from the resilient mount 17, a guide tube 39 extends throughthe inside of the threaded spindle 31. The guide tube has a mountingflange 41 with a mounting surface 43 for the mount 17. As a result, theguide tube is supported in the axial direction and in the radialdirection with respect to the mount 17. In addition, the guide tube isconnected by its mounting flange 41 to the housing 21 of the rotarydrive. The mount 17 has an elastomeric body 45, so that the guide tube39, the actuator 19, and the first spring collar 13 have a limitedfreedom of resilient movement.

The guide tube 39 has a cup-shaped expansion 47 to hold a resilientmount 49 for the piston rod 5, so that the mount 49 of the piston rodcan be supported against the guide tube by a fastener 55 such as a nut.The outside diameter of the piston rod 5 is smaller than the insidediameter of the guide tube 39 and the spring rate of the secondresilient mount 49 is lower than that of the elastomeric body 45. As aresult, the piston rod can move relative to the first mount 17 by way ofthe second mount 49 of the spring strut but requires no separateattachment to the vehicle body.

The guide tube 39 also provides a support function for the threadedspindle 31 of the rotary drive. For this purpose, the guide tube has afirst rolling bearing 51 for the threaded spindle 31. A second rollingbearing 53, which is supported on the bottom side of the mounting flange41, centers the rotor 27 and the upper end of the threaded spindle 31with respect to the guide tube 39.

FIGS. 2A and 2B show two design variants pertaining to the design of theguide tube 39, of the rotor 27, and of the housing 21 with the end part23. In FIG. 2A, the housing 21 and the end part 23 form a singlestructural unit, which is connected by fastening means 57 to themounting flange 41 of the guide tube. The second rolling bearingarrangement 53 for the threaded spindle 31 on the rotor side is realizedin the form of two bearings, one underneath, the other above, the endpart 23. These bearings can be designed as angular-contact ball bearingsin an “X” or “O” arrangement, for example. The advantage of thisembodiment over that of FIG. 1 is that is easier to manufacture theguide tube 39 and the housing 21. FIG. 2A also shows a thrust stop 59,which is attached to the guide tube 39 and which goes into effectagainst the upper end surface of the cylinder when the piston rod 5reaches a defined point during its inward travel.

FIG. 2B shows a second variant, in which the bearing arrangement of therotor 27 and of the threaded spindle 31 is based on the use of needlebearings. In addition, the guide tube 39 is connected by the end part 23to the mounting bearing 17. So that the bearings can be easily installedor removed, the guide tube 39 is divided at a certain point along itslength. A first guide tube section 39 a extends from the cup-shapedexpansion 47 to the lower bearing 51 of the threaded spindle. A secondguide tube section 39 b supports the bearing 51 and a spacer sleeve 61,which extends up as far as an upper bearing 63 of the threaded spindle31. The mounting on the rotor side is accomplished by a first bearing 53a between the rotor and the guide tube 39 and by a second bearing 53 bon the lower end part 65 of the housing 21. Thus the two end parts 23,65 of the housing 21 surround the rotor 27, which is fixed in the axialdirection by the two bearings 53 a, 53 b.

Because of the use of a guide tube 39 which is separate from the pistonrod 5, the vibration damper 3 can be removed from the spring carrierregardless of the design of the guide tube and/or of the housing simplyby disconnecting the fastener 55. There is no need to remove any of theother parts of the spring carrier.

Thus, while there have shown and described and pointed out fundamentalnovel features of the invention as applied to a preferred embodimentthereof, it will be understood that various omissions and substitutionsand changes in the form and details of the devices illustrated, and intheir operation, may be made by those skilled in the art withoutdeparting from the spirit of the invention. For example, it is expresslyintended that all combinations of those elements and/or method stepswhich perform substantially the same function in substantially the sameway to achieve the same results are within the scope of the invention.Moreover, it should be recognized that structures and/or elements and/ormethod steps shown and/or described in connection with any disclosedform or embodiment of the invention may be incorporated in any otherdisclosed or described or suggested form or embodiment as a generalmatter of design choice. It is the intention, therefore, to be limitedonly as indicated by the scope of the claims appended hereto.

1. A spring carrier for mounting a spring strut to a vehicle body, thecarrier comprising: a vibration damper comprising a cylinder and apiston rod which is axially guided in the cylinder; a first springcollar, a second spring collar, and a spring located between the springcollars; an actuator comprising a nut and a threaded spindle surroundingthe piston rod, the actuator being driven to change the relative axialposition of the spring collars; a guide tube extending coaxially betweenthe piston rod and the threaded spindle, the guide tube being configuredto support the threaded spindle in a fixed axial position relative tosaid guide tube; a first resilient mount fixed to the guide tube formounting the guide tube to the vehicle body; and a second resilientmount between the piston rod and the guide tube, whereby the piston rodcan move relative to the first resilient mount.
 2. The spring carrier ofclaim 1 wherein the first and second resilient mounts each have a springrate, the spring rate of the second resilient mount being lower than thespring rate of the first resilient mount.
 3. The spring carrier of claim1 wherein the guide tube comprises a cup-shaped section which receivessaid second resilient mount.
 4. The spring carrier of claim 1 whereinthe cup-shaped section has a circumferential surface which receives thefirst resilient mount.
 5. The spring carrier of claim 1 wherein thecircumferential surface extends both axially and radially.
 6. The springcarrier of claim 1 wherein the actuator comprises a rotary drive whichrotates the spindle in order to move the nut axially.
 7. The springcarrier of claim 6 further comprising at least one bearing whichsupports the spindle against the guide tube.
 8. The spring carrier ofclaim 1 wherein the guide tube has an axis and is divided transverselywith respect to said axis into two pieces.
 9. The spring carrier ofclaim 1 wherein the actuator comprises a housing which is fixed to theguide tube.
 10. The spring carrier of claim 1 further comprising athrust stop fixed inside the guide tube, the thrust stop limiting travelof the piston rod into the cylinder.
 11. The spring carrier of claim 1wherein the first resilient bearing comprises an elastomeric material.12. The spring carrier of claim 1 wherein the second resilient bearingcomprises an elastomeric material.
 13. The spring carrier of claim 1wherein the first spring collar is connected to the guide tube.
 14. Thespring carrier of claim 13 wherein the first spring collar is formed asone piece with the guide tube.
 15. The spring carrier of claim 1,wherein the guide tube comprises a mounting flange having a mountingsurface, and the first resilient mount is disposed on the mountingsurface.
 16. The spring carrier of claim 1, wherein the guide tubecomprises a first rolling bearing configured for supporting the threadedspindle.
 17. The spring carrier of claim 16, further comprising a rotorand second rolling bearing configured for centering the rotor and anupper end of the threaded spindle with respect to the guide tube.
 18. Aspring carrier for mounting a spring strut to a vehicle body, thecarrier comprising: a vibration damper comprising a cylinder and apiston rod which is axially guided in the cylinder; a first springcollar, a second spring collar, and a spring located between the springcollars; an actuator comprising a nut and a threaded spindle surroundingthe piston rod, the actuator being driven to change the relative axialposition of the spring collars; a guide tube extending coaxially betweenthe piston rod and the threaded spindle; a first resilient mount fixedto the guide tube for mounting the guide tube to the vehicle body; and asecond resilient mount between the piston rod and the guide tube,whereby the piston rod can move relative to the first resilient mount;wherein the first spring collar is connected to and formed as one piecewith the guide tube.